The invention relates to an energization coil device, preferably intended for use in a micromotor of the electromagnetic type, and to a method of making such a device.
It also relates to a micromotor that is fitted with such a device and which is intended for use in many kinds of applications where electromagnetically controlled power transducers need to be highly miniaturized. These applications include for instance horology, robotics, informatics, electronic apparatus for reproducing sound and images, aeronautics, aerospace and biomedical engineering.
This type of motor is called micromotor because, as will become apparent hereinafter, some of its components have minute dimensions, of the order of one micron (10.sup.-6 meter).
Like any electromagnetic motor, such micromotors comprise a first, stator-forming part and a second, rotor-forming part which is mobile in relation to the first. The rotor generally comprises a permanent magnet. In addition, these motors are generally provided with a plurality of energization coils each formed by a winding of electrical conductor. Such coils are magnetically coupled to the rotor and are electrically connected to an electronic control circuit that provides them with current pulses, known as drive pulses, that enable the rotor to be set in motion.
With a view to improving the miniaturization of such electromagnetic motors, it has already been proposed to produce coils in one plane, by means of spiral windings, such coils, termed "pancake coils" because of their coplanar arrangement, having little thickness. In this case, the rotor is produced in the form of a thin, axially magnetized disc which sets up, in the air gap of the magnetic circuit, axial fields extending through the coils, with the latter being arranged in a plane parallel to the rotor.
The first coils of this type were made of very fine copper wire. They were difficult to make and to connect to one another and to the control circuit, and were therefore hardly ever used because the cost of manufacturing them was very high.
More recently, it has been suggested, as described for example in U.S. Pat. No. 4,733,115, to produce coils on a printed circuit. Whilst satisfactory for making small motors, this technique cannot unfortunately be used in the production of micromotors as it does not enable coils to be made having sufficiently fine turns and hence the motor to be efficient.
To resolve this problem, it has also been suggested, in published Swiss patent application 668 160, to produce energization coils on a silicon plate, also termed a semiconductor substrate, in accordance with integrated circuit technology.
This technology offers many advantages over the printed circuit one since with it coils can be produced with turns formed by an aluminium conductor having an extremely low height and width, of the order of 2.multidot.10.sup.-6 meter (2 .mu.m) and having a resistance in the region of 2000 ohms. And because of this very high resistance the battery current can be limited to a value under one milliampere thereby enabling the driving device, particularly in horological applications, to be associated with a power source of conventional voltage in the region of 1.5 volts.
Moreover, with this technology it is possible to produce coil devices, i.e. modules comprising a substrate and several coils produced in pancake fashion thereon, having a thickness K (FIG. 1) of about 280.multidot.10.sup.-6 meter (280 .mu.m).
It will thus be appreciated that with such dimensions it does become possible to talk of miniaturization and of "micro"-motors particularly suited to applications such as horology or biomedical engineering.
However, it has now been found that such micromotors with integrated coils are clearly of inadequate efficiency, with the result that it was not feasible to consider putting them into production and on the market.
Besides, in view of the diversity of fields of application open to these motors, it would be desirable for these motors to operate either as unidirectional or bidirectional stepping motors or as unidirectional or bidirectional continuous rotation motors, at will.
If the motor described in the above Swiss patent application can reasonably be expected to be used as a stepping motor, it must however be acknowledged that it cannot at will be used as a continuous rotation motor or as a bidirectional motor.
This is because this type of motor is single-phased, and therefore would, for one thing, require highly complex and hence costly electronics if it were required to operate as a bidirectional motor. For another, the control of the rotor's position would necessitate resorting to feedback loops that involve sophistications that are equally onerous if the motor were required to operate as a continuous rotation motor.